Also known as Stevens Pass Tunnel and GN Cascade #15. In 1900, a 2.6 mile tunnel was built by Great Northern to eliminate 8 switchbacks and avoid winter weather hazards caused by over 50' of snow during the winter including avalanches. Unfortunately, this tunnel was still too high to avoid the winter weather. "On March 1, 1910, an avalanche at Wellington destroyed two Great Northern trains and killed 96 people. It was one of the worst railroad disasters in American history and closed the route for three weeks. On January 22, 1916, an avalanche struck a passenger train near Corea, killing eight people and injuring several others. To keep trains on schedule and bolster public confidence, Great Northern added more snow sheds along the route, increasing the annual cost of maintenance and repair." [HistoryLink] To reduce the winter hazards, a new 7.8 mile tunnel was built 501' (or 500' or 502', depending on the source) below the first tunnel. This new tunnel was completed in 1929, and it remains the longest railroad tunnel in the United States.
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| New Cascade Tunnel booklet, p4 |
"Due to the tunnel's length it has a rather problematic handicap, even today, of requiring ventilation of the shaft for up to 45 minutes. As a result Cascade is somewhat of a bottleneck on the BNSF system." The first ventilation system for the 1929 tunnel required an hour to clear the fumes produced by diesels working hard to scale the 1.7% grade from west to east. Today's fans can clear the tunnel in 20 minutes. "Train speeds today for BNSF freights and Amtrak passenger trains are held to 25 mph. One still has to wonder, however, why Burlington Northern did not exercise its ownership of nearby Snoqualmie Tunnel after the Milwaukee Road abandoned its main line through this region in 1980. Using that bore, which was the best engineered tunnel across the Cascade range, would have saved BN and BNSF millions in maintenance costs and liability." [American-Rails]
The grade is 1.6% and takes 30 minutes to clear the exhaust fumes according to Cascade Tunnel Ventilation. Another eastbound train must wait for the exhaust fumes to be blown out of the tunnel. But a westbound train does not have to wait because the exhaust of the previous eastbound train will stay in front of the westbound train. The exhaust plume of the westbound train leaves the tunnel with the train so neither the next eastbound nor westbound train is delayed.
In a discussion on the Trainorders forum, a former Chief Dispatcher for BN who was in charge of the line through the Cascade Tunnel said that the Tunnel Ventilation issue being a limiting factor on line capacity is a bunch of Horsefeathers. If it was a problem, then adding a mid-tunnel door like the Mount MacDonald Tunnel on CP has would solve the problem at a reasonable cost. The problem is the gradient through the tunnel and the distance between the sidings at either end. If the freight trains were the length of the Empire Builder and powered the same amount, you could operate a lot more trains per day through the tunnel. Where some problems with ventilating occur, they happen because the Dispatcher doesn't begin the ventilation promptly. This can happen because the Dispatcher is distracted by things happening elsewhere on his district, or if he (she) just isn't paying attention. And then there is the need for MOW to have track time, not just on the tunnel itself, but also anywhere between Skykomish and Wenatchee. [Trains, search for "2009 9:25"]
To build the 1929 tunnel, a work tunnel 8' high and 9' wide was first built and 21 connecting passages were dug to the main bore so that there was 42 working faces. 1,750 skilled workmen from around the country were hired to staff three shifts that worked seven days a week for 35 months. The blasting holes were 8' deep. After a blast the loose rock was cleared out using ore cars in the working tunnel. Each round took five hours. The tunnel was dug through granite, but they still used timber shoring. Even with the shoring, there were deaths due to rock slides. The concrete lining was constructed by placing reusable forms over the timbers and pouring concrete over them. Because of the length of the tunnel; cars filled with the correct ratio of cement, sand and gravel were hauled to a mixing plant at the face of the concrete work. "Some 923,000 cubic yards of rock and earth were removed from the bore, replaced by 264,000 cubic yards of concrete as lining for the tunnel." [HistoryLink]
HistoryLink has several photos of the 1929 construction.
The tunnel was electrified, but they had significant reliability issues with the electrification. One source indicated the system was not properly designed. As soon as the railroad finished converting to diesels in 1956, the electrification was replaced by a ventilation system at the east portal.
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